1. Field of the Invention
The present invention relates to a refrigeration system and more particularly to a refrigeration system able to achieve a temperature under 6 degrees in Kelvin from the combination of a main-refrigerator and a sub-refrigerator.
2. Description of the Related Art
A conventional refrigeration system 100, as shown in FIG. 4, is disclosed in U.S. Pat. No. 4,891,951. In the refrigeration system 100, a compression portion 101 which is formed by a bellows 111 is in fluid communication with an expansion portion 105 which is formed by a bellows 112 via a heat radiation apparatus 102, a heat generator 103, a condenser 104 and a conduit 110. The bellows 111, 112 are connected to rods 113, 114, respectively. Rods 113, 114 are driven, with a predetermined phase difference, by a driver 115. Thus, a refrigerating machine C is constituted and a very low temperature is generated at the expansion portion 105.
In a vacuum casing 117, a vessel 107 and the refrigerating machine C are positioned, except for the driver 115. An amount of liquid helium 106 is stored in the vessel 107 and a vapor phase 116 is defined above the liquid helium 106. A substance 118 to be cooled is immersed in the liquid helium 106. The vessel 107 is in fluid communication with the condenser 104 via a first conduit 108 and a second conduit 109.
In the conventional refrigeration system 100, a stroke of the bellows 111 is larger than a stroke of the bellows 112, and the bellows 111, 112 are made of metal members. Therefore, fatigue fracture easily occurs in the bellows 111.